What is a mechanical multimeter?

What is a mechanical multimeter? 

( 1 ) Mechanical multimeter structure general mechanical multimeter consists of meter head ( magnetoelectric type ), gear shift switch, mechanical zero adjustment device, and zero adjustment appliance, a stylus, socket, etc. According to the form of rotary switch can be divided into two categories : a single rotary switch type, MF201, MF91, MF47, MF500, and so on; the other is the double rotary switch type, which represents the model MF500.

Take the MF47 Knife as an example.

1,Circuit section.

The multimeter is composed of five circuits, the meter head or the meter head circuit, which is used for indicating the measuring result and the voltage divider circuit, which is used for measuring the intersection, dC voltage; shunt circuit for measuring DC current; battery Nulling potentiometer; for measuring resistance; the measurement selection circuit is used to select the gear range.

 2,Meter head.

 The meter head adopts the magnetoelectric microammeter as the meter head. The interior of the meter head is composed of upstream and downstream wires and magnets. When the small current passes through the meter head, the electromagnetic induction is generated, and the coil rotates under the action of the magnetic field and drives the pointer to deflect. The deflection angle of the pointer depends on the magnitude of the current through the meter. Since the wire diameter of the head coil is relatively small, the current allowed is very small. In practical application, in order to meet the needs of a larger range, a shunt and step-down circuit are arranged inside the multimeter to complete the measurement of various physical quantities.

3.Dial.

The first scale line is the electrical barrier reading, its right end is " 0 " and the left end is " ( infinity ) ", and the scale line is not uniform, reading should be read from the right to the left, that is, the closer to the left end of the needle, the greater the value. The second and third lines are AC voltage, DC voltage and DC current reading, the left end is " 0 ", and the right end is the maximum reading. According to the difference of the range switch, even if the needle is placed in the same position, the value of the voltage and current indicated is not the same. The fourth is the AC voltage reading line, which is designed to improve the accuracy of small voltage reading. The fifth line is the transistor magnification ( HRE ). The sixth and seventh lines are the reading lines measuring the load current and the load voltage. The eighth line is the reading line of the audio level ( dB ).

The MF47 multimeter is equipped with a reflector, which can reduce the visual error.

4. Readout of the switch.

Measure resistance : switch to RX 1 ~ RX 10k gear. Measuring AC voltage : transfer switch to 10 ~ 1000V gear. Measuring DC voltage : transfer switch to 0.25 ~ 1000V gear. If the voltage is measured, the pen will be inserted into the 2500V jack. Measure DC current : switch to 0. 25 ~ 250 mA gear. If the large current is measured, the " positive " ( red ) pen should be inserted into the " 105A " hole, and the " negative " ( black ) stylus should also be inserted in the original position. Measure the transistor magnification, shift the switch first to ADJ adjust the zero, so that the pointer to the right zero, and then the gear switch to the hFE block, the transistor is inserted into the NPN or PNP socket, and read the value of the fifth line, that is, 2-pole amplification times the sensitivity value. An AC voltage block should be used for the measurement of audio level dB. ( 2 ) Before using a multimeter, you should pay attention to whether the needle is in the " ( infinity ) " position, and if the needle is not in the position the screwdriver adjusts the mechanical zeroing knob to position the gauge needle at infinity. Note : the zeroing button can only be trimmed half a turn, otherwise it may be damaged so that it can not be adjusted.

 Before measuring, we should first make clear the physical quantity of the test, and dial the switch to the corresponding gear, at the same time, we should also consider the connection method of the good pen; then the test is carried out to avoid the damage of the multimeter due to misoperation. Before using different ranges of resistance, the positive and negative stylus should be docked first, and the " zero adjustment potentiometer " should be adjusted, otherwise the measured resistance error is too large.

Note : every time you change the block, you have to make a zero adjustment.

This article is from ALLICDATA ELECTRONICS LIMITED.